A traveler arrived in a city to find no living inhabitants, but many crows eating the flesh of the dead.

He said to them "You vile barbarian fowl! What cause have you to kill and eat the people of this town? You have slain young and old alike. Have you no sense of decency?"

"You accuse us falsely" Said one old crow. "They once had peace and plenty, but they coveted each others' riches, to include nests and mates. These people banqueted on stolen food, fornicated, and fought among themselves until there was nothing left to eat and nothing left to steal. Just because you find us picking dead flesh it doesn't make us the cause of death."

It is often the corruption within rather than attackers from outside that cause a civilization to fall.